(1) Field of the Invention
The present invention relates to an improvement for high speed durability of pneumatic tires, for instance, high performance low profile pneumatic tires adapted to run at high speeds.
(2) Related Art Statement
In general, high performance low profile pneumatic tires of this type have a so-called aspect ratio [(a tire section height "H").div.(a tire section width "S")] in a range of 0.35 to 0.6, and each have a belt reinforcing structure in which an auxiliary layer is provided between a belt layer and a tread to cover the belt layer especially for improving high speed durability. As conventional belt reinforcing structures, there are belt reinforcing structures as shown in FIGS. 6 and 7. In tires having such belt reinforcing structures, the other construction is the same as that of ordinary pneumatic radial tires.
The belt reinforcing structure 1 shown in FIG. 6 uses, as a belt 2, rubberized cords such as steel cords or organic fiber cords having a high modulus of elasticity. Auxiliary layers 5-1 and 5-2 so called cap layers or strip layers are provided between the belt 2 and a tread, not shown, to cover the belt 2. Each of the auxiliary layers 5-1 and 5-2 is formed by spirally and intimately winding a single rubberized organic thermally shrinkable fiber cord 7 (for instance, a nylon cord) substantially in parallel to a tire circumferential direction, and is arranged in such an area as to cover at least tire widthwise edge portions 2a of the belt layer 2. The auxiliary layers 5-1 and 5-2 shown in FIG. 6 are cap layers covering the entire belt layer 2 between the opposite edge portions 2a. Alternatively, strip layers (not shown) covering near the edge portions 2a only may be used solely or in combination with a cap layer as mentioned above. As shown in FIG. 6, the cords are conventionally spirally wound in a double layer construction such that the cord has a starting end 7a in the vicinity of one edge portion 2a of the belt layer 2 and a terminal end 7b near the other edge portion 2a of the belt layer 2. Alternatively, as shown in FIG. 7, there is a tire in which cords 7 are arranged such that a starting end 7a of the cord 7 is positioned at one of the edge portions or a central portion 2b of a belt 2, and a terminal end 7b is positioned at the central portion 2b or the other edge portion 2a of the belt 2.
However, when a low profile high performance tire having the starting end 7a or the terminal end 7b of the cord 7 arranged near the central portion 2b of the belt 2 runs at high speeds, the tread central portion undergoes such a large repeated deformation strain in that it is swelled outwards in a tire radial direction due to a centrifugal force and is deformed inwards in the radial direction under a high ground contact pressure at a ground contacting area. Ultimately, a rubber surrounding the starting end 7a or the terminal end 7b is fatigued and peeled, thereby conspicuously deteriorating high speed durability.
Further, when a tire having the starting end 7a or the terminal end 7b of the cord located near the edge portion 2a of the belt 2 rounds a curve at high speeds, the starting end 7a or the terminal end 7b undergoes a large repeated deformation strain, so that the surrounding rubber is fatigued to ultimately cause peeling thereof.